In the related art, an RPTV (rear projection television) which projects on a large-size screen from a projector unit set behind the screen is generally known (JP-A-2003-114479). RPTV has widely spread due to its lower unit cost per screen size than that of a plasma or liquid crystal televisions. However, it is disadvantageous that the projector unit set behind the screen increases the thickness.
Therefore, an RPTV which is thinned by restraining the increase in thickness due to the length of the projector lens by bending the projector lens to be set in the projector unit into a roughly V shape has been proposed (JP-A-2000-187274).
The projector lens of Patent Document 2 has an optical path converting means such as a prism that bends the optical axis of image light that has passed through a first optical lens group forming the projector lens at a predetermined angle to make the image light on the bent optical axis incident on the second optical lens group.
For RPTVs, cost reduction has been demanded, and many parts are plastic-made molded parts. Particularly, holder parts for holding the lens and prism need high accuracy. To attach parts for holding such optical parts and optical parts to be attached to the holder parts, means for positioning by fitting a positioning pin and a positioning hole is used.
However, to bend a complicated optical path as described above, many tilt surfaces are used since only right-angle surfaces with excellent moldability cannot form the part shape. Therefore, when positioning projections extending perpendicularly to a surface of the outer surface of the molded part which is not orthogonal to the opening and closing direction of a mold for forming the molded part are formed on this surface, a part of the positioning projections becomes undercut and makes it impossible to extract the molded item from the mold.
Therefore, in the related art, as shown in FIG. 11, when molding or after molding, a positioning pin 100 prepared in advance is molded as an insert, post-insert, or outsert part. This positioning pin has a columnar shape whose embedded portion 102 into a part 101 projects parallel to the mold opening and closing direction, and the front end portion 103 that fits in a positioning hole of the other part has a columnar shape extending and projecting perpendicularly to an inclined plane that is not orthogonal to the mold opening and closing direction. By using such a positioning pin having a shape whose line passing through the center of the embedded portion 102 and the center of the front end portion 103 is not straight (non-axisymmetric shape), the positioning pin 100 is molded integrally on the surface 106 orthogonal to the mold opening and closing direction.
However, the positioning pin is non-axisymmetric and complicated in shape, so that the pin cannot be accurately formed, and to obtain high accuracy, the processing costs increase. In addition, in insert, post-insert, or outsert molding, the positioning pin 100 must be formed separately, and this increases the costs further.